Contrail shadows sometimes appear counter-intuitive. This one seems
cast by a low altitude bright light shining upwards and casting the
contrail shadow on a higher cloud.

The reverse is the case. The aircraft and its trail are high up and
seen through a lower level thin layer of cirrus haze. The Moon has
cast a shadow of the contrail downwards onto the haze layer. And quite
independently of aircraft and shadows, ice crystals in the haze layer
have created the 22º
halo.

Contrails
are clouds of small water droplets and ice crystals condensed from
the engine exhaust and from water vapour already in the air cooled
by rarefaction over the wings and fuselage.

Like other clouds they cast shadows. In the photograph the shadow
falls on a thin lower layer of cirrus cloud. We see the shadow from
the other side of the layer, like looking through the back of a screen.

The shadow appears to the right of the line of sight between the contrail
itself and the eye.